The invention is directed to an apparatus for intradermal implantation of a device to facilitate repeated, painless, safe, and reliable access to interstitial fluid, blood, or blood plasma for monitoring of blood borne or tissue analyte concentrations including but not limited to glucose, cholesterol, lactate, bilirubin, blood gases, ureas, creatinine, phosphates, myoglobin and hormones or delivery of drugs or other injectable agents such as chemotherapeutic agents, photosensitizing agents, hormones, vaccines, or radiological or other contrast agents.
There is now a large body of evidence that intensive management of blood sugars is an effective means to slow or even prevent the progression of diabetic complications such as kidney failure, heart disease, gangrene, and blindness. The design and development of a simple apparatus for obtaining interstitial fluid, blood or blood plasma samples without breaking the skin would be a large advancement in trying to improve diabetic patient compliance for monitoring blood glucose levels.
Maintaining blood glucose concentrations near normal levels in diabetic patients can only be achieved with frequent blood glucose monitoring so that appropriate actions can be taken, such as insulin injections, or sugar ingestion. Unfortunately the current methods of sensing are based on colorimetric or electro-enzymatic approaches that require a blood or interstitial fluid sample each time a reading is needed. Withdrawal of a blood or interstitial fluid sample currently requires invasive methods of penetrating the skin surface. These methods are both time-consuming and painful and therefore there is a significant lack of compliance among the diabetic population for monitoring their blood glucose levels for the recommended five or more times daily.
Several research groups have focused efforts on methods for minimally invasive withdrawal of (primarily) interstitial fluid including the use of electrical current, suction, penetration, microdialysis, and laser-assisted drilling of the stratum corneum. While these techniques have shown some preliminary promise, questions still remain as to the volume of fluid which can be obtained, the repeatability of samples obtained, and the lack of any significant improvement in skin trauma related to the sampling methods. Additionally, the accuracy of glucose measurements on such small samples of interstitial fluid will likely be highly sensitive to contaminants from sweat or dirt on the surfaces being sampled and requires development of new measurement technology appropriate for such small or low concentration samples. Therefore, the ability to directly withdraw interstitial fluid samples in an easy, reliable and safe manner would be a significant advance in minimally invasive sensing techniques.
Other groups are developing totally implantable sensors for measurement of blood or interstitial fluid glucose concentration. Normally, however, when a foreign body such as a medical implant is introduced into a host, the natural tendency of the surrounding tissue is to degrade or extrude the implant. If the host cannot eliminate the foreign body, a chronic inflammatory reaction results and the object is encapsulated in fibrous tissue with foreign body giant cells residing at the tissue-material interface. This capsule poses a difficult problem in the development of implanted sensing or sampling devices. In the case of interstitial fluid sampling, the fibrous capsule presents a mass transfer barrier and therefore limits the concentration of analyte reaching the collection site. Also, encapsulated implants may exhibit a significant lag time in the response to changes in blood glucose concentration. The ability of the capsule to limit mass transfer has been demonstrated in several studies (see, for example, Wood et al., Assessment of a Model for Measuring Drug Diffusion Through Implant-Generated Fibrous Capsule Membranes, Biomaterials. 16:957-9, (1995)).
In one aspect, the present invention is directed to a method and apparatus for analyte detection which substantially overcomes one or more of the problems due to the limitations and disadvantages of the related art. More specifically, in this aspect the present invention is directed to a transcutaneous implant, methods for implanting and using the transcutaneous implant and fluid withdrawal/delivery implements and replaceable components for use with the transcutaneous implant. In one embodiment of this aspect of the invention, the transcutaneous implant includes an access component to provide a stable dermal interface, a central housing disposed within the access component, a septum disposed within the central housing, and a filtration membrane disposed at a distal end of the central housing to promote mass transfer of analyte in bodily fluid into a reservoir formed by the filtration membrane, the septum and the central housing.
These and other features and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description and claims that follow.